Lyle Denniston has an extensive analytical post on the Citizens United case.  He also says this about timing:

It now appears that the Justices will take their first look at the case sometime in mid-June; it has not yet been formally scheduled for a private Conference of the Justices, but the earliest Conference where it might be on the table would be June 14.  If review is granted, the case might not be heard until December at the earliest, after the election, and not decided until next year.  If summary reversal is to be its fate, though, that could come before the Justices finish the current Term late next month.  Because of the Justices’ February order in the case, the state court ruling is on hold for the time being.